This Rapid-Transition grant will examine the role of nicotine dependence in fostering continued use of smokeless tobacco (SLT) among adults. SLT use has expanded rapidly over the last 15 years among young persons, and has emerged as a major health concern. Many adolescents who initiated SLT during this upsurge in SLT use are now adults, and now find themselves dependent on this form of tobacco. Most previous research has focused on initiation of use during adolescence; adult users are an understudied population. We propose to test the hypothesis that SLT use. Subject will be N=200 adults ages 18-45, including former, occasional, light, and heavy users of most oral snuff. The outcome measure in a moderation-mediation model regression analysis will be extent of SLT exposure as assessed with biological measures. The three dependent measures are as follows: (1) Nicotine dependence, assessed through self-report, will be tested s a mediating dependent variable. The other dependent variables will be factor scores representing (2) psychiatric function and personality, and (3) executive cognitive functioning. This research will provide useful information about the continuation of SLT use into adulthood, when the risk for adverse health effects might be thoroughly realized.